Method and apparatus for video coding

ABSTRACT

An apparatus for video decoding includes receiving and processing circuitry. The circuitry is configured to receive a bitstream including a syntax element associated with a parent coding unit (CU) in a picture indicating the parent CU is partitioned into a predefined set of child CUs without performing a recursive tree-structure-based partitioning, and process the child CUs according to the indication of the syntax element to reconstruct the picture. In an embodiment, at least two subdivisions need to be performed when the parent CU is partitioned using the recursive tree-structure-based partitioning in order to obtain the same set of child CUs. In an embodiment, at least one of the child CUs has a size larger than a minimum allowed CU size for partitioning the parent CU and includes no syntax element to indicate whether the at least one of the child CUs is to be further subdivided.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of U.S. ProvisionalApplication No. 62/852,853, “A Kind of Split Mode for Further VideoCoding” filed on May 24, 2019, and No. 62/857,162, “A Kind of Split Modefor Further Video Coding” filed on Jun. 4, 2019, which are incorporatedby reference herein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has specific bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth and/or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless compression and lossy compression, as well as a combinationthereof can be employed. Lossless compression refers to techniques wherean exact copy of the original signal can be reconstructed from thecompressed original signal. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is smallenough to make the reconstructed signal useful for the intendedapplication. In the case of video, lossy compression is widely employed.The amount of distortion tolerated depends on the application; forexample, users of certain consumer streaming applications may toleratehigher distortion than users of television distribution applications.The compression ratio achievable can reflect that: higherallowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Infra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is using reference data only from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding or decoding. In some examples, an apparatus for video decodingincludes receiving and processing circuitry. The circuitry is configuredto receive a bitstream including a syntax element associated with aparent coding unit (CU) in a picture indicating the parent CU ispartitioned into a predefined set of child CUs without performing arecursive tree-structure-based partitioning, and process the child CUsaccording to the indication of the syntax element to reconstruct thepicture. In an embodiment, at least two subdivisions need to beperformed when the parent CU is partitioned using the recursivetree-structure-based partitioning in order to obtain the same set ofchild CUs.

In an embodiment, at least one of the child CUs has a size larger than aminimum allowed CU size for partitioning the parent CU and includes nosyntax element to indicate whether the at least one of the child CUs isto be further subdivided. In an embodiment, the recursivetree-structure-based partitioning is a recursive partitioning based on abinary tee structure, a ternary tree structure, a quadtree structure, anextended quadtree structure, or a combination of two or more of thebinary tee structure, the ternary tree structure, the quadtreestructure, or the extended quadtree structure.

In an embodiment, the parent CU is a coding tree unit (CTU) partitionedfrom the picture, or is partitioned from a CTU that is partitioned fromthe picture. In an embodiment, the child CUs are CUs that are notfurther subdivided. For example, no syntax element associated with eachof the child CUs is transmitted in the bitstream for indicating whethereach of the child CUs is further subdivided. In an embodiment, at leastone of the child CUs is associated with a syntax element indicatingwhether the at least one of the child CUs is further subdivided.

In an embodiment, the child CUs have a same shape and size. In anembodiment, the child CUs have a square shape or a rectangular shape. Inan embodiment, the child CUs have a size of 8×8 samples. In anembodiment, the child CUs have different shapes or sizes. In anembodiment, the syntax element indicates a template describing how theparent CU is partitioned into the predefined set of child CUs.

In some examples, an apparatus for video encoding includes processingand transmitting circuitry. The circuitry is configured to partition aparent CU in a picture into a predefined set of child CUs withoutperforming a recursive tree-structure-based partitioning, and processthe child CUs to generate a bitstream including a syntax elementassociated with the parent CU that indicates the parent CU ispartitioned into the set of child CUs without performing the recursivetree-structure-based partitioning.

Aspects of the disclosure also provide non-transitory computer-readablemedia storing instructions which when executed by a computer for videodecoding cause the computer to perform the methods for video encoding ordecoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8A shows a coding tree unit (CTU) that is partitioned with aquadtree plus binary tree (QTBT) structure (820).

FIG. 8B shows the QTBT structure (820).

FIG. 9A shows a horizontal binary tree.

FIG. 9B shows a vertical binary tree.

FIG. 9C shows a horizontal center-side ternary-tree.

FIG. 9D shows a vertical center-side ternary-tree.

FIG. 10A shows a parent coding unit (CU) split into two M×(N/4) CUs andtwo (M/2)×(N/2) CUs.

FIG. 10B shows a parent CU split into two (M/4)×N CUs and two(M/2)×(N/2) CUs.

FIG. 11A shows a tree-structure based block partitioning process (1100A)according to an embodiment of the disclosure.

FIG. 11B shows a coding tree (1100B) corresponding to the partitioningprocess (1100A).

FIG. 12A shows a direct split mode based block partitioning process(1200A) according to an embodiment of the disclosure.

FIG. 12B shows another coding tree (1200B) corresponding to thepartitioning process (1200A).

FIG. 13A shows an example where a parent CU (1310) of a size of 16×32samples can be partitioned into 8 child CUs each having a size of 8×8samples.

FIG. 13B shows an example where another parent CU (1320) of a size of32×32 samples can be partitioned into 16 child CUs each having a size of8×8 samples.

FIG. 14A shows a parent CU (1410) having a size of 32×32 samples ispartitioned into the child CUs (1411-1414) having a size of 16×16samples.

FIG. 14B shows a first coding tree corresponding to a direct split modebased partitioning.

FIG. 14C shows a second coding tree corresponding to a quadtree basedpartitioning mode.

FIG. 15 shows a flow chart outlining a decoding process (1500) accordingto an embodiment of the disclosure.

FIG. 16 shows a flow chart outlining an encoding process (1600)according to an embodiment of the disclosure.

FIG. 17 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the tetminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture mernory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compress technology or standard. Specifically a profile can selectcertain tools as the only tools available for use under that profilefrom all the tools available in the video compression technology orstandard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder may receive video samples from a video source (501)(that is not part of the electronic device (520) in the FIG. 5 example)that may capture video image(s) to be coded by the video encoder (503).In another example, the video source (501) is a part of the electronicdevice (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand fhe relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may includetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use a inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictoninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Block Partitioning Structures 1. Quadtree Block PartitioningStructure

A block partitioning structure can be employed to produce a coding treethat includes a root node, non-leaf nodes, and leaf nodes. In someembodiments, by using a quadtree structure, a coding tree unit (CTU) canbe split into coding units (CUs) (leaf node CUs or leaf CUs in a codingtree) to adapt to various local characteristics. For example, the CTUcan be partitioned into intermediate CUs (non-leaf node CUs or non-leafCUs) with a quadtree split. An intermediate CU can be furtherpartitioned in a recursive way using the quadtree structure with arestriction of an allowable CU size.

In this disclosure, during a process where a CTU is partitioned into CUsbased as indicated by a coding tree, a CU refers to a leaf node CU in acoding tree, while an intermediate CU (between the CTU and the CUs inthe coding tree) refers to a non-leaf node CU in the coding tree.

A decision on whether to code a picture area using an inter-picture(temporal) or intra-picture (spatial) prediction is made at the leaf CUlevel. For a leaf CU to-be-coded with inter prediction, the leaf CU canbe further split, for example, into one, two, or four prediction units(PUs) according to a PU splitting type. Inside one PU, a same predictionprocess is applied and relevant information is transmitted to a decoderon a PU basis. Similarly, for a leaf CU to-be-coded with intraprediction, the leaf CU can be further partitioned for applyingdifferent intra coding modes.

After obtaining a residual block of a leaf CU by applying a predictionprocess, the leaf CU can be partitioned into transform units (TUs)according to another quadtree structure. As can be seen, there aremultiple partition conceptions including CU (leaf node CU), PU, and TU.In some embodiments, a CU or a TU can only be square shape, while a PUmay be square or rectangular shape. In some embodiments, one codingblock corresponding to a leaf CU may further split into four squaresub-blocks, and transform is performed on each sub-block, i.e., TU. Onecoding block corresponding to a leaf CU can be split recursively intosmaller TUs using a quadtree structure which is called residual quadtree(RQT).

At a picture boundary, in some embodiments, implicit quadtree split canbe employed so that a block will keep quad-tree splitting until the sizefits the picture boundary.

2. Quadtree Plus Binary Tree (QTBT) Block Partitioning Structure

In some embodiments, a quadtree plus binary tree (QTBT) structure isemployed. The QTBT structure removes the concepts of multiple partitiontypes (the CU, PU and TU concepts), and supports more flexibility forleaf CU partition shapes. In the QTBT block structure, a (leaf) CU canhave either a square or rectangular shape.

FIG. 8A shows a CTU (810) that is partitioned by using a QTBT structure(820) shown in FIG. 8B. The CTU (810) is first partitioned by a quadtreestructure. The resulting quadtree nodes are further partitioned by abinary tree structure or a quadtree structure. The quadtree splitting isrepresented as solid lines, while the binary tree splitting isrepresented by dashed lines. There can be two splitting types, symmetrichorizontal splitting and symmetric vertical splitting, in the binarytree splitting. The binary tree leaf nodes CUs can be used forprediction and transform processing without any further partitioning(e.g., no PUs in the leaf CUs). Accordingly, CU, PU and TU can have thesame block size in the QTBT coding block structure in the example ofFIG. 8A and FIG. 8B.

In some embodiments, a CU can include coding blocks (CBs) of differentcolor components. For example, one CU contains one luma CB and twochroma CBs in the case of P and B slices of the 4:2:0 chroma format. ACU can include a CB of a single color component. For example, one CUcontains only one luma CB or just two chroma CBs in the case of Islices.

The following parameters are defined for the QTBT partitioning scheme insome embodiments:

-   -   CTU size: the root node size of a quadtree.    -   MinQTSize: the minimum allowed quadtree leaf node size.    -   MaxBTSize: the maximum allowed binary tree root node size.    -   MaxBTDepth: the maximum allowed binary tree depth.    -   MinBTSize: the minimum allowed binary tree leaf node size.

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64,the MinBTSize (for both width and height) is set as 4×4, and theMaxBTDepth is set as 4. The quadtree partitioning is applied to the CTUfirst to generate quadtree leaf nodes. The quadtree leaf nodes may havea size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size).If the leaf quadtree node is 128×128, it will not be further split bythe binary tree since the size exceeds the MaxBTSize (i.e., 64×64).Otherwise, the leaf quadtree node could be further partitioned by thebinary tree. Therefore, the quadtree leaf node is also the root node forthe binary tree and it has the binary tree depth as 0.

When the binary tree depth reaches MaxBTDepth (i.e., 4), no furthersplitting is considered. When the binary tree node has a width equal toMinBTSize (i.e., 4), no further horizontal splitting is considered.Similarly, when the binary tree node has a height equal to MinBTSize, nofurther vertical splitting is considered. The leaf nodes of the binarytree are further processed by prediction and transform processingwithout any further partitioning (e.g., no PU partition). In anembodiment, a maximum CTU size is 256×256 luma samples.

In each splitting (i.e., non-leaf) node of the binary tree, one flag canbe signaled to indicate which splitting type (i.e., horizontal orvertical) is used. For example, 0 indicates a horizontal splitting and 1indicates a vertical splitting. For the quadtree splitting, there is noneed to indicate the splitting type since quadtree splitting can split ablock both horizontally and vertically to produce 4 sub-blocks with anequal size.

In some embodiments, the QTBT scheme supports the flexibility for theluma and chroma to have a separate QTBT structure. For example, for Pand B slices, the luma and chroma blocks in one CTU share the sane QTBTstructure. However, for I slices, the luma CTB is partitioned into CUsby a QTBT structure, and the chroma blocks are partitioned into chromaCUs by another QTBT structure. Thus, a CU in an I slice consists of acoding block of the luma component or coding blocks of two chromacomponents, and a CU in a P or B slice consists of coding blocks of allthree color components.

In some embodiments, inter prediction for small blocks is restricted toreduce memory access of motion compensation. For example, bi-predictionis not supported for 4×8 and 8×4 blocks, and inter prediction is notsupported for 4×4 blocks.

3. Ternary Tree (TT) Block Partitioning Structure

In some embodiments, a multi-type-tree (MTT) structure is used forpartitioning a picture. The MTT structure is a more flexible treestructure than the QTBT structure. In MTT, in addition to quad-tree andbinary-tree (horizontal or vertical), horizontal center-sideternary-tree and vertical center-side ternary-tree as shown in FIG. 9Cand FIG. 9D, respectively, are employed. Ternary tree partitioning cancomplement quad-tree and binary-tree partitioning. For example,ternary-tree partitioning is able to capture objects which locate in ablock center, while quad-tree and binary-tree splits crossing blockcenters. In an example, the width and height of partitions by ternarytrees are a power of 2 so that no additional transform partition isneeded.

For example, when the MTT structure is employed, a CTU can first besplit into four CUs by a quadtree structure. Then, each CU can befurther partitioned recursively by a quadtree structure, a binary treestructure, or a ternary tree structure. The partitioning may berestricted with CU sizes and split types of a parent CU. There are twosplitting types, symmetric horizontal splitting (FIG. 9A or FIG. 9C) andsymmetric vertical splitting (FIG. 9B and FIG. 9D), in the binary treeand ternary tree splitting. Accordingly, a parent CU can be split intotwo, three or four sub-CUs (or child CUs). Each CU can have a square orrectangular shape.

4. Extended Quadtree Tree Block Partitioning Structure

In some embodiments, a CTU can first be split into four CUs(intermediate CUs) by a quadtree structure. After the quadtree split,each CU (intermediate CU) can be further partitioned recursively by aquadtree structure, a binary structure, or an extended quadtree (EQT)structure witn the restrictions of a CU size and a split type of aparent CU. EQT partitioning indicates a parent CU can be split into fourCUs with different sizes. For example, a parent CU with a size of N by Msamples can be split into two M×(N/4) CUs and two (M/2)×(N/2) CUs, ortwo (M/4)×N CUs and two (M/2)×(N/2) CUs as shown in FIG. 10A and FIG.10B, respectively. There can be two splitting types, symmetrichorizontal splitting and symmetric vertical splitting, in the BT and EQTsplitting. A parent CU can be split into two or four sub-CUs (or childCUs). Each CU can have either a square or rectangular shape.

III. Direct Split Mode

In some embodiments, a direct split mode is employed for partitioning aparent CU into child CUs. As described, in tree-structure based blockpartitioning modes (e.g., block partitioning modes with a tree structureof QT, BT, TT, EQT, or a combination thereof), a CTU can be partitionedinto CUs (leaf CUs) by recursively applying partitioning of a treestructure. In contrast, in direct split mode, a parent CU (e.g., a CTUor an intermediate CU) can be directly partitioned into a predefined setof child CUs (e.g., intermediate CUs or leaf CUs) without going throughthe recursive partitioning process. One advantage of the direct splitmode is that signaling cost for describing how leaf CUs are partitionedfrom a CTU can be reduced.

FIG. 11A shows a tree-structure based block partitioning process (1100A)according to an embodiment of the disclosure. The partitioning process(1100A) is based on a quadtree structure, and includes steps from(S1101) to (S1104). As a result of the partitioning process (1100A), aparent CU (1110) is partitioned into 16 child CUs (1112).

At (S1101), the parent CU (1110) is provided. The parent CU (1110) canbe a CTU partitioned from a picture, or an intermediate CU (non-leaf CUin a coding tree) partitioned from a CTU. The CTU can be part of a sliceor tile partitioned from the picture. The parent CU (1110) can include acoding block (CB) of luma samples and two coding blocks (CBs) of chromasamples in some example. For example, the parent CU (1110) can have asquare shape, and have a size of 256, 128, 64, or 32 samples. The parentCU (1110) in FIG. 11A is shown to have a size of 128×128 samples.

At (S1102), the parent CU (1110) is subdivided into 4 sub-CUs(1111A-1111D) each having a size of 64×64 samples. At (S1103), thetop-left sub-CU (1111A) is further subdivided into 4 child CUs 1112 eachhaving a size of 32×32 samples. At (S1104), the remaining sub-CUs(1111B-1111D) are each further partitioned into 4 child CUs (1112). Intotal, five partitions of the quadtree structure are performed in theprocess (1100A).

FIG. 11B shows a coding tree (1100B) corresponding to the partitioningprocess (1100A). Each node in the coding tree (1100B) corresponds to oneof the parent CU (1110), the sub-CUs (1111A-1111D), or the child CUs(1112). Thus, identical numerals are assigned to the respective nodes inFIG. 11B as used in FIG. 11A.

When the partitioning process (1100A) is employed in an encoder, syntaxelements indicating partitioning of the parent CU (1110) can be signaledin a bitstream generated from the encoder. In an example, at the parentCU (1110) level, a flag can be include into the bitstream to indicatewhether the parent CU (1110) forms a CU (leaf CU) or whether the parentCU (1110) is split into four equally-sized blocks (the sub-CUs(1111A-1111D)) corresponding to square luma sample blocks. When theparent CU (1110) is split, for each of the resulting sub-CUs(1111A-1111D), another flag can be transmitted specifying whether thesub-CU (1111A-1111D) represents a CU (leaf CU) or whether the sub-CU(1111A-1111D) is further split into four equally-sized blocks. Thisrecursive subdivision can be continued until none of the resultingblocks is further divided.

When the above partitioning signaling method is employed, as shown FIG.11B, corresponding to each of the nodes (1110, 1111A-1111D, and 1112), aflag (1120) indicating whether the respective node is to-be-partitionedis generated and transmitted in the bitstream. For example, the flag ofbit 1 can indicate a further partition, while the flag of bit 0 canindicate no further partition to be performed. In total, 21 flags (1120)or bits can be transmitted for signaling the partitioning of the parentCU (1110) into the 16 child CUs (1112).

In an example, a minimum size of CUs (leaf CUs) can be signaled in asequence parameter set (SPS) in the bitstream carrying the child CUs(1112). For example, the minimum size of CUs can range from 8×8 lamasamples to a size of a CTU. When the minimum CU size is reached in thepartitioning process 1100A, no splitting flags are transmitted for thecorresponding blocks. Instead, it is inferred that these blocks with theminimum CU size are not further split. In the FIG. 11B example, if theminimum CU size is defined to be 32×32 samples, no split flags aretransmitted for each child CU (1112). In such a scenario, 5 flags (1120)in total (fewer fits) can be transmitted for signaling how the parent CU(1110) is partitioned.

FIG. 12A shows a direct split mode based block partitioning process(1200A) according to an embodiment of the disclosure. The partitioningprocess (1200A) can be performed without using tree-structure basedpartitioning. The process can include steps from (S1201) to (S1202). Asa result of the portioning process (1200A), a parent CU (1210) identicalto the parent CU (1110) is partitioned into 16 child CUs (1212)identical to the child CUs (1112).

At (S1201), the parent CU (1210) is provided. The parent CU (1210) canbe a CTU partitioned from a picture, or an intermediate CU partitionedfrom a CTU. The parent CU (1210) can include a CB of luma samples andtwo CBs of chroma samples. For example, the parent CU (1210) can have asquare shape, and have a size of 256, 128, 64, or 32 samples. The parentCU (1210) in FIG. 12A is shown to have a size of 128×128 samples.

At (S1202), the parent CU (1210) is directly subdivided into 16 childCUs (1212). In total only one partition is conducted compared with 5partitions in the FIG. 11A example.

FIG. 12B shows another coding tree (1200B) corresponding to thepartitioning process (1200A). A root node (1210) corresponds to theparent CU 1210 in FIG. 12A, and 16 leaf nodes (1212) correspond to the16 child CUs (1212) in FIG. 12A. Identical numerals are used for therespective nodes in FIG. 12B and the respective CUs in FIG. 11A.

Corresponding to the direct split mode partitioning process (1200A),syntax elements indicating partitioning of the parent CU (1210) can besignaled in a bitstream generated from an encoder. Different from therecursive partitioning in the FIG. 11A or 11B example where split flagsare generated for each level of blocks in the coding tree (1100B), onesplit flag (1220) at the root level is generated and signaled for thedirect split mode partitioning. In the FIG. 11B example, 21 flags intotal (or 5 flags when the child CUs 1112 have the minimum CU size) aresignaled. In contrast, only 1 flag (1220) is signaled in FIG. 12Bexample. Thus, signaling cost for indicating block partitioning isreduced when direct split mode is employed.

Considering there can be different predefined sets of child CUs (ordifferent templates), a syntax element in place of the split flag (1220)may use multiple bits (more than 1 bit) to indicate which set of childCUs is indicated. In some examples, direct split mode may be combinedwith tree-structure-based partitioning. Thus, more bits may be used todistinguish the split mode from the tree-structure-based split modes. Insome examples, configuration of whether to use direct split mode may besignaled in the respective bit stream. For example, a syntax element maybe used to turn on or turn of the direct split mode. Accordingly,additional bits may be signaled for configuration purpose. However, insome examples, when the direct split mode is employed for partitioning aparent CU, the number of child CUs can be dozens of predefined targetCUs. Savings of the signaling cost can still be significant in suchscenarios.

Generally, a parent CU can be split into a predefined set of child CUswhen direct split mode is applied. The parent CU can be a CTU or can bean intermediate CU (non-leaf CU) partitioned from a CTU. A CTU can bepartitioned from a slice or a tile of a picture.

In some embodiments, the child CUs in direct split mode can be CUs (leafCUs) for each of which an encoder determines whether inter prediction orintra prediction is to be applied. Accordingly, no split flag issignaled for the child CUs defined as CUs.

In some other embodiments, when direct split mode is used to partition aparent CU, a resulting child CU can be an intermediate CU (non-leaf CU)that can be further subdivided into CUs (leaf CUs) or smallerintermediate non-leaf CUs. In such a scenario, a split flag can besignaled for each of the child CUs to indicate whether the respectivechild CU is to be further split. In some examples, the child CUs canhave a same size or different sizes. When a child CU has size of aminimum CU size, signaling of the respective split flag can be omitted.

In some examples, direct split mode can be used for transform blockpartitioning. For example, direct split mode can be used forpartitioning a CU into target transform blocks. For example,partitioning based on direct split mode can replace a residual quadtree.

In some embodiments, a parent CU can be subdivided into several childCUs (or sub-CUs) with a same shape and a same size. The size and shapeof the child CUs can be predefined. A syntax element indicating thepredefined child CUs can be associated with the parent CU andtransmitted in a bitstream. For example, to obtain several child CUs of8×8 samples, a 32×32 parent CU can be split five times with a quadtreestructure to obtain 16 child CUs. In contrast, the direct split modesupports partitioning the 32×32 CU into 8×8 child CUs directly. A syntaxelement can be associated with the parent CU to indicate thepartitioning.

In some embodiments, corresponding to the scenario where a predefinedchild CU having a specific size and shape, parent CUs with differentsizes can be partitioned into different number of child CUs. FIG. 13Ashows an example where a parent CU (1310) of a size of 16×32 samples canbe partitioned into 8 child CUs each having a size of 8×8 samples. FIG.13B shows an example where another parent CU (1320) of a size of 32×32samples can be partitioned into 16 child CUs each having a size of 8×8samples.

In an embodiment, for a direct split mode, the predefined samesize/shape child CUs can have a square shape. Partitioning with thedirect split mode can replace a recursive partitioning process with aquadtree structure. In an example, the child CUs have a size of 8×8samples. In an embodiment, the child CUs can have a rectangular shape.Partitioning with the direct split mode can replace a recursivepartitioning process with a BT, TT, or EQT structure.

In some embodiments, a parent CU can be subdivided into several childCUs with different shapes and Sizes. For example, different templatescan be defined in advance each corresponding to a different set of childCUs having various sizes and/or shapes. Each template can be indicatedwith a syntax element signaled in a bitstream.

In some embodiments, templates can be employed for both the cases ofchild CUs having a same size and shape, and child CUs having differentsizes and shapes. Each such template is assigned a syntax element forsignaling the particular manner of partitioning. Depending on the numberof options of different templates, the bits used for indicating thedirect split mode partitioning can vary.

When direct split mode is employed at an encoder side, the encoder candetermine whether to use a tree-structure based partitioning mode or adirect split mode to partition a parent CU according to arate-distortion optimization based algorithm. For example, differentpartitioning methods can be tested and the one with the best codingefficiency can be selected. In some embodiments, some fast algorithmscan be employed to make a partitioning decision based on property of acoding area. For example, for an intra coded slice including largeamount of details and textures, the slice can be partitioned into intracoded blocks with small sizes to improve codding efficiency.Accordingly, based on characteristics of the slice, a direct split modecan be selected for directly partitioning parent CUs into large numberof child CUs to save signaling cost associated with block partitioning.

In the examples of FIG. 12A and FIG. 12B, the parent CU (1210) ispartitioned into a large number of child CUs (1212). For example, toobtain a same number of the child CUs (1212), at least two subdivisionsneed to be performed when the parent CU (1210) is partitioned using therecursive tree structure based partitioning. In contrast, FIGS. 14A-14Cshow an example where a parent CU 1410 is partitioned into 4 child CUs(1411-1414). One partition in a direct split mode based partitioning canobtain the 4 child CUs (1411-1414), while one partition in a quadtreebased partitioning can also obtain the 4 child CUs. In such a scenario(small number of child CUs), employment of direct split mode can stillsave block partitioning related signaling cost compared withtree-structure based partitioning.

As shown in FIG. 14A, the parent CU (1410) has a size of 32×32 samples,and is partitioned into the child CUs (1411-1414) having a size of 16×16samples. FIG. 14B shows a first coding tree corresponding to the directsplit mode based partitioning. The nodes (1410D, and 1411D-1414D)correspond to the parent CU (1410) and the child CUs (1411-1414),respectively. One flag 1421 can be signaled for indicating thepartitioning.

FIG. 14C shows a second coding tree corresponding to the quadtree basedpartitioning mode. The nodes (1410T, and 1411T-1414T) correspond to theparent CU (1410) and the child CUs (1411-1414), respectively. Five flags(1431/1432) can be signaled for indicating the partitioning (assumingthe size, 16×16 sample, of the child CUs (1411T-1414T) is larger than aminimum allowed CU size). As shown, the partitioning based on the directsplit mode incurs fewer bits for indicating block partitioning than thatbased on tree-based partitioning. If the minimum CU size is defined tobe 16×16 samples, the flags (1432) can be omitted, and the partitioningin FIG. 14B and FIG. 14C would incur a same number of split flag (1 flagfor each split mode).

IV. Examples of Direct Split Mode Based Block Partitioning Processes

FIG. 15 shows a flow chart outlining a decoding process (1500) accordingto an embodiment of the disclosure. During the process (1500), blocks ofsamples partitioned by a direct split mode can be processed andreconstructed. The process (1500) can be used in the reconstruction of apicture or a region of a picture. In various embodiments, the process(1500) are executed by processing circuitry, such as the processingcircuitry in the terminal devices (210), (220), (230) and (240), theprocessing circuitry that performs functions of the video decoder (310),the processing circuitry that performs functions of the video decoder(410), and the like. In some embodiments, the process (1500) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1500). The process starts at (S1501) and proceeds to(S1510).

At S(1510), a bitstream is received that includes a syntax elementassociated with a parent CU in a picture. The syntax element canindicate the parent CU is partitioned into a predefined set of child CUswithout performing a recursive tree-structure-based partitioning. In anexample, the parent CU is partitioned into a large number of child CUs,and at least two subdivisions need to be performed if the recursivetree-structure-based partitioning is used to partition the parent CU inorder to obtain the same set of child CUs.

In an example, at least one of the child CUs has a size larger than aminimum allowed CU size for partitioning the parent CU and includes noindication of whether the at least one of the child CUs is to be furthersubdivided. This can save signaling cost when compared with a scenariowhere a tree-structure-based partitioning is used and a split flag isassociated with a block (larger than a minimum allowed CU size) toindicate Whether the block is to be further split.

In various examples, the recursive tree-structure-based partitioning canbe a recursive partitioning based on a binary tee structure, a ternarytree structure, a quadtree structure, an extended quadtree structure, ora combination of two or more of the binary tee structure, the ternarytree structure, the quadtree structure, or the extended quadtreestructure. Or, the recursive tree-structure-based partitioning can be arecursive partitioning based on a tree structure other than the treestructure listed above.

In various examples, the parent CU can be a CTU partitioned from thepicture, or can be partitioned from a CTU that is partitioned from thepicture. In an example, the child CUs are CUs that are not furthersubdivided. For example, such CUs are entities for which the encoderdetermines whether to apply an inter picture prediction or an intrapicture prediction. Such CUs can be further divided in some examples forpurpose of applying inter prediction modes or intra perdition modes.

In an example, no syntax element is transmitted for each of the childCUs in the bitstream for indicating whether each of the child CUs isfurther subdivided. This can save signaling cost compared with scenarioswhere tree-structure-based partitioning is employed, and flagsindicating whether to further split are signaled.

In an example, at least one of the child CUs is associated with a syntaxelement indicating whether the at least one of the child CUs is furthersubdivided. For example, the child CUs resulting from the direct splitmode can be further split, and flags are signaled to indicate furthersplits are to be performed or not to be performed.

In an example, the child CUs have a same shape and size. In an example,the child CUs have a square shape or a rectangular shape. In an example,the child CUs have a size of 8×8 samples. In an example, the child CUshave different shapes or sizes. In an example, the syntax elementindicates a template describing how the parent CU is partitioned intothe predefined set of child CUs that may have a same or different sizeand shape.

At (S1520), the child CUs are processed according to the indication ofthe syntax element to reconstruct the picture. For example, the decoderinterprets the syntax element to know how the parent CU is partitionedinto the child CUs, and accordingly locates and interprets syntaxelements in the bitstream corresponding to the child CUs. Subsequently,based on the determined syntax elements, the decoder performs a seriesof decoding operations to reconstruct CUs corresponding to the childCUs. For example, the decoding operations can include inversequantization and inverse transform for determining residual signals,determination of prediction blocks according to motion information orintra prediction mode, combination of residual signals with predictionblocks to reconstructed blocks of different color components. Byreconstructing CUs in the picture, the picture can be reconstructed. Theprocess (1500) can proceed to (S1599) and terminates at (S1599).

FIG. 16 shows a flow chart outlining an encoding process (1600)according to an embodiment of the disclosure. During the process (1600),a direct split mode can be employed to partition a parent CU into apredefined set of child CUs. The process (1600) can be used in theencoding of a picture. In various embodiments, the process (1600) areexecuted by processing circuitry, such as the processing circuitry inthe terminal devices (210), (220), (230) and (240), the processingcircuitry that performs functions of the video encoder (303), theprocessing circuitry that performs functions of the video encoder (503),and the like. In some embodiments, the process (1600) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1600). The process starts at (S1601) and proceeds to (S1610).

At (S1610), a parent CU in a picture can be partitioned into apredefined set of child CUs without performing a recursivetree-structure-based partitioning. In an example, the parent CU ispartitioned into a large number of child CUs, and at least twosubdivisions need to be performed if the recursive tree-structure-basedpartitioning is used to partition the parent CU in order to obtain thesame set of child CUs.

In various examples, the recursive tree-structure-based partitioning canbe a recursive partitioning based on a binary tee structure, a ternarytree structure, a quadtree structure, an extended quadtree structure, ora combination of two or more of the binary tee structure, the ternarytree structure, the quadtree structure, or the extended quadtreestructure. Or, the recursive tree-structure-based partitioning can be arecursive partitioning based on a tree structure other than the treestructure listed above.

In various examples, the parent CU can be a CTU partitioned from thepicture, or can be partitioned from a CTU that is partitioned from thepicture. In an example, the child CUs are CUs that are not furthersubdivided. For example, such CUs are entities for which the encoderdetermines whether to apply an inter picture prediction or an intrapicture prediction. Such CUs can be further divided in some examples forpurpose of applying inter prediction modes or intra perdition modes.

In an example, the child CUs have a same shape and size. In an example,the child CUs have a square shape or a rectangular shape. In an example,the child CUs have a size of 8×8 samples. In an example, the child CUshave different shapes or sizes.

At (S1620), the child CUs are processed to generate a bitstreamincluding a syntax element associated with the parent CU that indicatesthe parent CU is partitioned into the set of child CUs withoutperforming the recursive tree-structure-based partitioning.

In an example, at least one of the child CUs has a size larger than aminimum allowed CU size for partitioning the parent CU and includes nosyntax element to indicate whether the at least one of the child CUs isto be further subdivided. This can save signaling cost when comparedwith a scenario where a tree-structure-based partitioning is used and asplit flag is associated with a block to indicate whether the block isto be further split.

In an example, no syntax element is transmitted for each of the childCUs in the bitstream for indicating whether each of the child CUs isfurther subdivided. This can save signaling cost compared with scenarioswhere tree-structure-based partitioning is employed, and flagsindicating whether to further split are signaled.

In an example, at least one of the child CUs is associated with a syntaxelement indicating whether the at least one of the child CUs is furthersubdivided. For example, the child CUs resulting from the direct splitmode can be further split and flags are signaled to indicate furthersplits are to be performed. In an example, the syntax element indicatesa template describing how the parent CU is partitioned into thepredefined set of child CUs. The process (1600) can proceed to (S1699),and terminates at (S1699).

V. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 17 shows a computersystem (1700) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 17 for computer system (1700) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1700).

Computer system (1700) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photottraphic images obtain from a still imagecamera), video (such a two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1701), mouse (1702), trackpad (1703), touchscreen (1710), data-glove (not shown), joystick (1705), microphone(1706), scanner (1707), camera (1708).

Computer system (1700) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1710), data-glove (not shown), or joystick (1705), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1709), headphones(not depicted)), visual output devices (such as screens (1710) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each or without tactilefeedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1700) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1720) with CD/DVD or the like media (1721), thumb-drive (1722),removable hard drive or solid state drive (1723), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1700) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1749) (such as, tbr example USB ports of thecomputer system (1700)); others are commonly integrated into the core ofthe computer system (1700) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1700) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1740) of thecomputer system (1700).

The core (1740) can include one or more Central Processing Units (CPU)(1741), Graphics Processing Units (GPU) (1742), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1743), hardware accelerators for certain tasks (1744), and so forth.These devices, along with Read-only memory (ROM) (1745), Random-accessmemory (1746), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1747), may be connectedthrough a system bus (1748). In some computer systems, the system bus(1748) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1748),or through a peripheral bus (1749). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1741), GPUs (1742), FPGAs (1743), and accelerators (1744) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1745) or RAM (1746). Transitional data can be also be stored in RAM(1746), whereas permanent data can be stored for example, in theinternal mass storage (1747). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1741), GPU (1742), massstorage (1747), ROM (1745), RAM (1746), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1700), and specifically the core (1740) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1740) that are of non-transitorynature, such as core-internal mass storage (1747) or ROM (1745). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1740). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1740) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1746) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1744)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

ASIC: Application-Specific Integrated Circuit

AVS: Audio Video Coding Standard

AVS: Audio Video Coding Standard

BMS: Benchmark Set

BT: Binary Tree

CANBus: Controller Area Network Bus

CD: Compact Disc

CfP: Call for Proposals

CPUs: Central Processing Units

CRT: Cathode Ray Tube

CTBs: Coding Tree Blocks

CTU: Coding Tree Unit

CU: Coding Unit

DVD: Digital Video Disc

EQT: Extended Quadtree

FPGA: Field Programmable Gate Areas

GOPs: Groups of Pictures

GPUs: Graphics Processing Units

GSM: Global System for Mobile communications

HDR: High Dynamic Range

HEVC: High Efficiency Video Coding

HRD: Hypothetical Reference Decoder

IC: Integrated Circuit

JEM: joint exploration model

JVET: Joint Video Exploration Team

JVET: Joint Video Exploration Team

LAN: Local Area Network

LCD: Liquid-Crystal Display

LTE: Long-Term Evolution

MV: Motion Vector

OLED: Organic Light-Emitting Diode

PBs: Prediction Blocks

PCI: Peripheral Component Interconnect

PLD: Programmable Logic Device

PUs: Prediction Units

RAM: Random Access Memory

ROM: Read-Only Memory

SDR: standard dynamic range

SEI: Supplementary Enhancement Information

SNR: Signal Noise Ratio

SSD: solid-state drive

TT: ternary tree

TUs: Transform Units,

USB: Universal Serial Bus

VTM: VVC Test Model

VUI: Video Usability Information

VVC: Versatile Video Coding

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding at a video decoder,comprising: receiving in a bitstream an enabling flag associated with aparent coding unit (CU) in a picture, the enabling flag indicatingwhether a direct split mode is enabled for partitioning the parent CUinto a predefined set of child CUs without performing a recursivetree-structure-based partitioning; in response to receiving the enablingflag indicating that the direct split mode is enabled for partitioningthe parent CU into the predefined set of child CUs without performingthe recursive tree-structure-based partitioning, receiving in thebitstream a syntax element associated with the parent CU indicating howthe parent CU is partitioned into the predefined set of child CUs in thedirect split mode without performing the recursive tree-structure-basedpartitioning, a number of the predefined set of child CUs resulting fromthe partition indicated by the syntax element being greater than 4; andprocessing the child CUs according to the indication of the syntaxelement to reconstruct the picture.
 2. The method of claim 1, wherein atleast two subdivisions need to be performed when the parent CU ispartitioned using the recursive tree-structure-based partitioning inorder to obtain the same set of child CUs.
 3. The method of claim 1,wherein at least one of the child CUs has a size larger than a minimumallowed CU size for partitioning the parent CU and includes no syntaxelement to indicate whether the at least one of the child CUs is to befurther subdivided.
 4. The method of claim 1, wherein the recursivetree-structure-based partitioning is a recursive partitioning based on abinary tree structure, a ternary tree structure, a quadtree structure,an extended quadtree structure, or a combination of two or more of thebinary tree structure, the ternary tree structure, the quadtreestructure, or the extended quadtree structure.
 5. The method of claim 1,wherein the parent CU is a coding tree unit (CTU) partitioned from thepicture, or is partitioned from a CTU that is partitioned from thepicture.
 6. The method of claim 1, wherein the child CUs are CUs thatare not further subdivided.
 7. The method of claim 6, wherein no syntaxelement associated with each of the child CUs is transmitted in thebitstream for indicating whether each of the child CUs is furthersubdivided.
 8. The method of claim 1, wherein at least one of the childCUs is associated with a syntax element indicating whether the at leastone of the child CUs is further subdivided.
 9. The method of claim 1,wherein the child CUs have a same shape and size.
 10. The method ofclaim 1, wherein the child CUs have a square shape or a rectangularshape.
 11. The method of claim 1, wherein the child CUs have a size of8×8 samples.
 12. The method of claim 1, wherein the child CUs havedifferent shapes or sizes.
 13. The method of claim 1, wherein the syntaxelement indicates a template describing how the parent CU is partitionedinto the predefined set of child CUs.
 14. A method of video encoding ata video encoder, comprising: partitioning, with a direct split mode, aparent coding unit (CU) in a picture into a predefined set of child CUswithout performing a recursive tree-structure-based partitioning; andprocessing the child CUs to generate a bitstream including: an enablingflag associated with the parent CU that indicates the direct split modeis enabled for partitioning the parent CU into the predefined set ofchild CUs without performing the recursive tree-structure-basedpartitioning, and following signaling of the enabling flag thatindicates the direct split mode is enabled for partitioning the parentCU into the predefined set of child CUs without performing the recursivetree-structure-based partitioning, a syntax element associated with theparent CU that indicates how the parent CU is partitioned into the setof child CUs in the direct split mode without performing the recursivetree-structure-based partitioning, a number of the predefined set ofchild CUs resulting from the partition being greater than
 4. 15. Anapparatus of video decoding, comprising circuitry configured to: receivein a bitstream an enabling flag associated with a parent coding unit(CU) in a picture, the enabling flag indicating whether a direct splitmode is enabled for partitioning the parent CU into a predefined set ofchild CUs without performing a recursive tree-structure-basedpartitioning; in response to receiving the enabling flag indicating thatthe direct split mode is enabled for partitioning the parent CU into thepredefined set of child CUs without performing the recursivetree-structure-based partitioning, receive in the bitstream a syntaxelement associated with the parent CU indicating how the parent CU ispartitioned into the predefined set of child CUs in the direct splitmode without performing the recursive tree-structure-based partitioning,a number of the predefined set of child CUs resulting from the partitionindicated by the syntax element being greater than 4; and process thechild CUs according to the indication of the syntax element toreconstruct the picture.
 16. The method of claim 1, wherein the numberof the predefined set of child CUs resulting from the partitionindicated by the syntax element is equal to or greater than
 8. 17. Themethod of claim 1, wherein the number of the predefined set of child CUsresulting from the partition indicated by the syntax element is equal toor greater than
 16. 18. The method of claim 1, wherein the number of thepredefined set of child CUs resulting from the partition indicated bythe syntax element is equal to or greater than
 32. 19. The method ofclaim 1, wherein in response to the direct split mode being disabled,determining that the parent CU is partitioned into child CUs byperforming the recursive tree-structure-based partitioning.
 20. Themethod of claim 14, further comprising: selecting one of the recursivetree-structure-based partitioning and the direct split mode to partitionthe parent CU, the selection being based on a rate-distortionoptimization based algorithm or a property of signals in the parent CU.